A construction machine such as an excavator includes a working implement with a bucket, an arm, and a boom. The construction machine is equipped with a plurality of hydraulic pumps as a drive source of a hydraulic cylinder for operating the working implement.
Patent Literature 1 discloses a hydraulic circuit including a merging valve for switching a merged state and a divided state for working fluid discharged from a first hydraulic pump and working fluid discharged from a second hydraulic pump. When the first hydraulic pump and the second hydraulic pump are in the merged state, the working fluid discharged from the first hydraulic pump and the working fluid discharged from the second hydraulic pump are merged by the merging valve and are distributed to a plurality of hydraulic cylinders. When the first hydraulic pump and the second hydraulic pump are in the divided state, a boom cylinder is operated by the working fluid discharged from the first hydraulic pump, and a bucket cylinder and an arm cylinder are operated by the working fluid discharged from the second hydraulic pump.
When the working fluid is distributed to the plurality of hydraulic cylinders while the first hydraulic pump and the second hydraulic pump are in the merged state, a phenomenon occurs in which the flow rate of the working fluid supplied to the hydraulic cylinder receiving a small load is larger than the flow rate of the working fluid supplied to the hydraulic cylinder receiving a large load. For that reason, when an operation device is operated so that an operator of the construction machine operates the working implement while the first hydraulic pump and the second hydraulic pump are in the merged state, the working fluid is not supplied to the hydraulic cylinder at the flow rate in response to the operation amount of the operation device, and hence the operability of the operation device is degraded.
Patent Literature 2 discloses a technique in which a pressure compensating valve is provided between a main operation valve and a hydraulic actuator so as to equalize a pre/post-differential pressure of the main operation valve connected to each of a plurality of hydraulic cylinders in the merged state of a first hydraulic pump and a second hydraulic pump. Since each of the main operation valves has a uniform pre/post-differential pressure, the working fluid is supplied to the hydraulic cylinder at the flow rate in response to the operation amount of the operation device, and hence degradation in operability of the operation device is suppressed.